A tire currently used these days mainly comprises a tread intended to provide contact with the ground, this tread generally being reinforced by a crown reinforcement which is positioned radially on the inside of the tread. The crown reinforcement is able to give the crown the rigidities, in the three dimensions, that it needs for the running of the tire. The crown reinforcement also limits the radial expansion of a carcass reinforcement, generally made up of one or more plies of radial reinforcing elements. When the tire is mounted so as to become functional, it contains an inflation gas, inflated to a nominal pressure. The carcass reinforcement, during the use of the tire within reasonable limits, deforms both statically and when running. The carcass reinforcement is generally anchored in each bead to a reinforcing ring. The beads provide contact with the seat and flange of the rim on which the tire is mounted.
Transmission of mechanical load between the tire and the rim, which load is the result of the inflation, compression and running of the tire, and sealing of this tire are provided by the distribution and the magnitude of the forces of contact between the bead and the rim seats and rim flanges. Good tire behaviour both from the standpoint of endurance and from the standpoint of the properties conferred on the vehicle equipped with it, and a good mounting rim quality/price ratio have led to the adoption of a ratio of rim width to maximum axial tire width of around 0.7. It is known that this ratio is merely a compromise and that a certain number of tire properties, for example roadholding are improved by the use of a rim allowing a higher ratio; conversely, other properties can be improved, of course at the expense of the former properties, by mounting on a narrow rim, namely by having a ratio, as defined hereinabove, of around 0.40 or less.
Patent FR 1 267 264, which seeks to give a tire the mutually contradictory properties of comfort, roadholding, low rolling resistance and high resistance to wear, teaches the outlines a solution that entails giving the carcass reinforcement a structure that is effectively capable of opposing transverse flexibility without detracting from radial structural flexibility. This structure is obtained by superimposing, in the carcass reinforcement, with the initial structure of radial reinforcing elements, a secondary structure of inextensible circumferential reinforcing elements. This secondary structure may moreover modify the shape of the sidewalls of the tire, which shape is dictated by the equilibrium meridian profile of the mid-axis of the carcass reinforcement: circumferential and inextensible reinforcing elements of a diameter substantially equal to or less than the diameter of the rim flange, and arranged radially and axially on the inside of the radial elements of the carcass reinforcement allow this reinforcement to have a meridian profile which is almost horizontally tangential to the annular anchoring element of the carcass reinforcement.
This principle is adopted again in U.S. Pat. No. 3,486,547, and more particularly in an application to a mounting rim width that is markedly smaller than the width of the tread, the ratio of rim width to minimum axial width of tire being 0.41 in the example given.
Although it has attractive properties, this tire is not without its disadvantages, in terms of the ability to steer the vehicle fitted with it. Indeed, the reinforcing reinforcer intended to stabilize the secondary structure has, in the circumferential direction, a very high extension rigidity and a markedly lower compression rigidity. The difference in the moduli of the reinforcing reinforcer according to whether it is being worked in extension or in compression in the radial direction means that the outer lower part experiences significant ovalization when such a tire is subject to a vertical loading. When transverse loading is applied to such an axially loaded tire, the tire exhibits a non-linear response depending on whether the load applied was or was not sufficient to re-tension the part that became compressed during the ovalization.
In order to overcome these disadvantages, U.S. Pat. No. 6,626,217 proposes to dissociate in the above tire the part that can be considered as actually working like a tire from the part that can be considered as acting like a rim. The corresponding running set is made up of a tire, of a narrow rim of which the width is at most equal to 50% of the maximum axial width of the tire inflated to its service pressure, and of two adapters providing the connection between the mounting rim and the beads of the tire, the adapters being made of rubber compositions that are reinforced and elastically deformable at least in the two, radial and axial, directions.
While this running set allows a marked improvement in comfort and resistance to kerbing of the vehicle fitted with it, it is not entirely satisfactory as far as the steering of the vehicle is concerned.
Application WO 92/01576 describes a tire assembly comprising a tire mounted on a rim. A removable protector made of a reinforced rubber circular annulus is inserted between the bead of the tire and the rim. This protector is intended to protect the beads of the tire from the phenomenon of heating during running.
Application FR 2,491,836 describes an adapter positioned between the rim and each bead of a tire and intended to make tire fitting/removal easier.